1. Field of the Invention
The present invention relates to a device for adjusting the amount of ink supplied for use in a printing press.
2. Description of the Prior Art
In presses such as offset printing presses, an impression is in general made by mounting a form plate on a plate cylinder and by supplying ink to the printing area on the form plate by a form roller rotated in a state wherein it is in contact with the form plate while feeding dampening water to the area on the form plate other than the printing area by a dempening roller rotated in a state wherein it is in contact with the form plate. The printing area on the form plate has dots formed on it at fixed intervals over a predetermined area of the form plate with a printing image having a high density represented by larger dots and a printing image of a low density represented by smaller dots. Therefore, the amount of ink supplied to the printing area on the form plate is determined by the ratio of dots of various sizes to the predetermined area of the form plate, i.e., the value of the area ratio of the printing area.
In this press, the amount of ink supplied to the form plate by the form roller is adjusted by an ink amount adjusting device such as that shown in FIG. 7. The ink amount adjusting device includes an ink blade 1, ink adjusting screws 2, ink blade position detectors (potentiometers or the like) 3, ink blade position control motors 4, and a housing 1A. The ink blade 1 is desposed along the longitudinal direction of an ink fountain roller 5. The ink adjusting screws 2 are respectively disposed for each of the longitudinal divided areas of the ink blade 1, these areas of the ink blade 1 being moved toward or away from the ink fountain roller 5 by the corresponding ink adjusting screws 2 so as to adjust the gap between the ink blade 1 and the ink fountain roller 5 through which ink is supplied to the form plate. The position of the ink blade 1 relative to the ink fountain roller 5 which is adjusted by the ink adjusting screws 2 is detected by the corresponding ink blade position detectors 3. The position of the ink blade 1 is controlled by the corresponding control motors 4 through the ink adjusting screws 2 on the basis of the values detected by the corresponding ink blade position detectors 3.
The rotation of each of the control motors 4 is transmitted to the corresponding ink adjusting screw 2 through a gear 4A fixed to the output shaft of the control motor 4 and a gear 2A fixed to the ink adjustig screw 2. The position of the ink blade 1 is transmitted to each of the ink blade position detectors 3 through the ink adjusting screw 2, the gear 2A, a gear 3A, a clutch 6 and a disk 3B to the ink blade position detector 3. The gear 3A is mounted on the input shaft of the ink blade position detector 3 in such a manner that it can race thereon. The disk 3B is fixed to the input shaft of the ink blade position detector 3.
In the known ink amount adjusting device of the above-described type, the position of the ink blade 1 is manually zeroed approximately once a week by a large number of ink adjusting screws 2 which may be incorporated in a printing press, the total number thereof being, for example, 120. Reference numeral 7 denotes an adjusting knob provided on each of the ink adjusting screws 2.
Such a known ink amount adjusting device, however, involves a disadvantage is that it requires zero adjustment of each of the ink blade position detectors 3 which is conducted after the position of the ink blade 2 has been zeroed by the ink adjusting screws 2. Each ink blade position detector 3 is zeroed by disengaging the clutch 6, by manually adjusting the ink blade position detector 3 so that its indicator rests exactly on "a position which represents zero", and by engaging the clutch 6 after the position of the ink blade 1 has been zeroed by the ink adjusting screws 2.
More specifically, in the known ink amount adjusting device, it is necessary to zero the ink blade position detectors separately after the position of the ink blade has been zeroed by the ink adjusting screws. Thus, a great deal of time is required for zero adjustment.